Air-sensitive and/or moisture-sensitive materials, such as alkali metal alcoholate and hydrides, are packaged for storage and transport purposes under protective gas, e.g. argon or nitrogen, in plastic foil, which is then hermetically sealed. The plastic foil used is for instance polyethylene (PE)-foil. Also air-sensitive and/or moisture-sensitive materials can be packaged in soluble polyurethane (PU)-foils or in soluble foils of ethylene-ethylvinyl-acetate (EVA). However PU foils have the disadvantage that decomposition products which are health hazards can result during the dissolution of the PU foils. In the case of EVA foils it is disadvantageous that they can be dissolved only in toluene which is a material hazardous to health and only at temperatures higher than approx. 60.degree. C. In order to release the material packaged therein in a chemical reactor, one is obligated either to use toluene as a solvent as well as to insure that the material is heated to these temperatures, or the foil package has to be opened and the material has to be introduced into the reactor via a lock.